The present invention is related to a blind-slat control mechanism, including a pair of first rope ladders mounted between an upper and lower beams of a Venetian blind for a plurality of slats to be equidistantly abutted against for location thereby, and the upper ends of the first rope ladders are located at mounting seats adapted at both inner lateral sides of the upper beam to control the rotation of the slats in different angles thereby. A pull cord, led through cord-passage holes of each slat, is wound through a pulley seat disposed at one end of the upper beam to control the folding or unfolding operation of the slats thereby. Sliding guide plates are disposed at the corresponding side of both mounting seats thereof for a pair of second rope ladders and a driving cord to be fixedly attached thereto respectively, and the second rope ladders, each bestriding the bottommost slat thereof in a U-shaped form, have a plurality of positioning steps alternatively astride the slats in odd or even number. A hook ring and a pivoting hole are disposed at the other end of the upper beam for the driving cord to pass and suspend downwards there-from; whereby, via the linkage operation thereof, the driving cord is simply pulled to actuate the movement of the sliding guide plates and synchronically draw upwards the second rope ladders therewith in an easy and fast manner, effectively avoiding the slant of the slats due to uneven pulling force applied thereto to achieve the best using condition thereof.
Please refer to FIG. 1. A conventional blind slat control mechanism is made up of a Venetian blind 10 having a first rope ladder 11 and a second rope ladder 12 sequentially mounted to a plurality of slats 13 and respectively bestriding a lower beam 14 into U-shaped forms. Positioning slide posts 151 and a first and second pulley seats 152, 153 are respectively disposed at both ends of an upper beam 15 for both ends of the first and second rope ladders to wind there-through and extend downwards there-from. In practical use, the first rope ladder 11 is pulled downwards to draw up the odd-numbered or even-numbered slats 13, piling up the slats 13 in pairs to augment the light-passable space as shown in FIG. 2. When the second rope ladder 12 is pulled downwards, the slats 13 will keep gathering up from bottom to top in a sequence. A mounting seat with an adjustment member is adapted inside the upper beam 15 for retaining another rope ladder (without shown in the diagram) to adjust the rotation of the slats 13 in different angles.
There are some drawbacks to such conventional blind slat control mechanism. First, the first and the second rope ladders 11, 12 are suspended downwards from the same side of the upper beam 15. In practical use, it's easy to misjudge the two rope ladders 11, 12 and mix up the two in operation. Besides, in case pulling force is unevenly applied onto both ends of the first or the second rope ladders 11, 12, the slats 13 can easily get tilted and cause the inconvenience in operation thereof. Second, the first rope ladder 11 is wound through the lower beam 14 thereof. In case of a great pulling force applied thereto, the first rope ladder 11 tends to raise upwards the lower beam 14 and sequentially gather up each slat 13 from bottom to top, losing the function to pile up the slats 13 in pairs. Thus, the operation of the first rope ladder 11 thereof is more difficult to control. Third, the first rope ladder 11, winding through the inner side of the lower beam 14, must first actuate the lower beam 14 before extending through the first pulley seat 152 to suspend downwards there-from, which can waste quite a lot of efforts and pains in the operation thereof. Fourth, the two positioning slide posts 151 and first/second pulley seats 152, 153 are mounted inside the upper beam 15 thereof for the first and the second rope ladders 11, 12 to wind there-through, which can increase the cost of material and make the assembly thereof more troublesome and tedious.